1. Field of the Invention
This invention relates to crystal oscillators and more particularly to accounting for differences among crystal oscillators.
2. Description of the Related Art
In traditional phase-locked loop (PLL) based crystal oscillator devices, slight variations in the internal crystal frequency between one crystal and another lead to a different frequency plan for each device to maintain the same output frequency. The frequency plan determines the divider values for the particular device, which in turn, determine the output frequency. Using different frequency plans for the same output frequency causes several problems. In programmable oscillators, if a customer has two oscillators on a printed circuit board or the same part on two boards that need to generate the same output frequencies, the customer has to measure/calculate the crystal frequency of each part and then calculate a separate frequency plan for each part. That is not only cumbersome, but also difficult on boards with limited processing power. For pin controlled parts, which are programmed during manufacturing for a particular frequency or frequencies that are pin selectable, a standard frequency plan cannot be used for programming the parts for the particular frequency or frequencies due to slight variations in the crystals.